The incorrect statement is:

🧠 Test Each Statement

The "incorrect" question — work through each.

🗺️ Walk Each Option

(1) $[\mathrm{Fe(H_2O)_6}]^{2+}$ vs $[\mathrm{Cr(H_2O)_6}]^{2+}$.

• Fe²⁺ ($\mathrm{d^6}$, high-spin with weak-field $\mathrm{H_2O}$): $\mathrm{t_{2g}^4 e_g^2}$ → 4 unpaired → μ ≈ 4.9 BM.
• Cr²⁺ ($\mathrm{d^4}$, high-spin): $\mathrm{t_{2g}^3 e_g^1}$ → 4 unpaired → μ ≈ 4.9 BM. Both ~4.9 BM. Correct. ✓

(2) $[\mathrm{Ni(NH_3)_4(H_2O)_2}]^{2+}$. Ni²⁺ is $\mathrm{d^8}$. With six donor atoms (4 N + 2 O), it's octahedral. $\mathrm{NH_3}$/$\mathrm{H_2O}$ are intermediate-field, so high-spin $\mathrm{d^8}$: $\mathrm{t_{2g}^6 e_g^2}$ → 2 unpaired → μ = $\sqrt{2(2+2)} = \sqrt{8} = 2.83$ BM. Correct. ✓

(3) "Ruby has Cr³⁺ ions occupying octahedral sites of beryl." Ruby is actually corundum ($\mathrm{Al_2O_3}$) with Cr³⁺ replacing Al³⁺ in octahedral holes. Beryl is the emerald host ($\mathrm{Be_3Al_2Si_6O_{18}}$). Incorrect — the wrong host name. ✗

(4) $[\mathrm{Co(NH_3)_5Cl}]^{2+}$ absorbs yellow → transmits violet (complementary). The complex appears violet. Correct. ✓

⚡ Ruby vs Emerald Host Crystals

| Gem | Host | Dopant | |---|---|---| | Ruby | $\mathrm{Al_2O_3}$ (corundum) | Cr³⁺ | | Emerald | $\mathrm{Be_3Al_2Si_6O_{18}}$ (beryl) | Cr³⁺ | | Sapphire | $\mathrm{Al_2O_3}$ (corundum) | Fe³⁺/Ti⁴⁺ |

Same dopant (Cr³⁺), different host crystal field → different colour.

⚠️ The Beryl/Corundum Swap

Ruby = corundum, NOT beryl. Emerald = beryl. Memorise this exchange — it's a textbook trap.

$\boxed{\text{Answer: (3) Ruby has Cr³⁺ in beryl — the wrong host crystal}}$